Arrhythmias

• What does heart block refer to?


  An obstruction in the electrical conduction system of the heart
• Where can obstruction in the heart's conduction system occur?

  At the sinoatrial node, atrioventricular node, Bundle of His, or bundle branches
• What specifically does atrioventricular heart block affect?


  The conduction between the atria and ventricles
• What is the range of severity for heart block?


  From first degree to complete (third degree) heart block
• What management is required for complete (third degree) heart block?

  Immediate management with a permanent pacemaker
• What is the definition of heart block?


  An obstruction in the electrical conduction system of the heart
• Why does SAN block rarely lead to symptoms?

  The atrioventricular node acts as a secondary pacemaker
• What are the symptoms of atrioventricular heart block?


  Fatigue, lightheadedness, syncope, shortness of breath, cardiac arrest, or sudden death
• Mechanism of first degree heart block?

  Prolonged conduction of electrical activity through the AV node
• How can first degree heart block be identified on an ECG?


  By finding a PR interval >200ms
• What are the causes of first degree heart block?


  • High vagal tone (e.g., athletes)
  • Acute inferior MI
  • Electrolyte abnormalities (e.g., hyperkalaemia)
  • Drugs (e.g., NHP-CCBs, beta-blockers, digoxin, cholinesterase inhibitors)
• What is the management for first degree heart block?


  It is benign and does not need treating, but underlying causes should be reversed
• What characterizes Mobitz Type I heart block?


  Progressive lengthening of the PR interval leading to a non-conducted QRS
• What is another name for Mobitz Type I heart block?


  Wenckebach phenomenon
• What are the causes of Mobitz Type I heart block?


  • MI (mainly inferior)
  • Drugs (beta/calcium channel blockers, digoxin)
  • Professional athletes (high vagal tone)
  • Myocarditis
  • Cardiac surgery
• What is the management for Mobitz Type I heart block?


  Generally asymptomatic and does not require specific management
• What characterizes Mobitz Type II heart block?


  Intermittent non-conducted P waves with a constant PR interval
• What is the usual mechanism for Mobitz Type II heart block?

  Conduction system failure, especially at the His-Purkinje system
• What are the causes of Mobitz Type II heart block?


  • Infarction (particularly anterior MI)
  • Surgery (mitral valve repair or septal ablation)
  • Inflammatory/autoimmune (rheumatic heart disease, SLE, systemic sclerosis, myocarditis)
  • Fibrosis (Lenegre's disease)
  • Infiltration (sarcoidosis, haemochromatosis, amyloidosis)
  • Medication (beta-blockers, calcium channel blockers, digoxin, amiodarone)
• What is the management for Mobitz Type II heart block?


  Definitive management is with a permanent pacemaker
• What occurs in complete (third degree) heart block?


  Atrial impulses fail to be conducted to the ventricles
• What does the ECG show in complete heart block?


  Severe bradycardia and complete dissociation between P waves and QRS complexes
• What are the risks associated with complete heart block?


  High risk of asystole, ventricular tachycardia, and cardiac arrest
• What are the causes of complete heart block?

  • Myocardial infarction (especially inferior)
  • Drugs acting at the AVN (beta blockers, dihydropyridine calcium channel blockers, adenosine)
  • Idiopathic fibrosis
• What is the management for complete heart block?


  Management is via the acute bradycardia guideline and requires a permanent pacemaker
• What is atrial fibrillation (AF) characterized by?


  Irregular and uncoordinated atrial contraction at a rate of 300-600 beats per minute
• How does the prevalence of AF change with age?


  It roughly doubles with each advancing decade of age
• What are the symptoms of atrial fibrillation?


  Palpitations, chest pain, shortness of breath, lightheadedness, and syncope
• How is atrial fibrillation diagnosed?


  By an ECG showing the absence of P waves and an irregularly irregular rhythm
• What are the classifications of atrial fibrillation?


  • Acute: lasts <48 hours
  • Paroxysmal: lasts <7 days and is intermittent
  • Persistent: lasts >7 days but is amenable to cardioversion
  • Permanent: lasts >7 days and is not amenable to cardioversion
  • Fast AF: rate =>100 bpm
  • Slow AF: rate <=60 bpm
• What are the cardiac causes of atrial fibrillation?


  • Ischaemic heart disease (most common cause in the UK)
  • Hypertension
  • Rheumatic heart disease (most common cause in less developed countries)
  • Peri-/myocarditis
• What are the non-cardiac causes of atrial fibrillation?


  • Dehydration
  • Endocrine causes (e.g., hyperthyroidism)
  • Infective causes (e.g., sepsis)
  • Pulmonary causes (e.g., pneumonia or pulmonary embolism)
  • Environmental toxins (e.g., alcohol abuse)
  • Electrolyte disturbances (e.g., hypokalaemia, hypomagnesaemia)
• What are the signs of atrial fibrillation?


  Irregularly irregular pulse rate, single waveform on jugular venous pressure, apical to radial pulse deficit, variable intensity first heart sound, and features suggestive of underlying causes
• What are the important differential diagnoses for atrial fibrillation?


  • Atrial Flutter
  • Supraventricular Tachycardia
  • Ventricular Tachycardia
  • Anxiety-driven presentations
• What is the definitive diagnosis for atrial fibrillation?


  12-lead ECG shows absence of P waves with an irregularly irregular rhythm
• What should be done if paroxysmal AF is suspected but not detected on standard ECG?


  Arrange ambulatory electrocardiography or cardiology referral
• What routine blood tests should be conducted for atrial fibrillation?

  • Look for reversible causes including infection (raised WCC or CRP)
  • Hyperthyroidism (raised T3/T4)
  • Alcohol use (raised MCV and GGT)
• What imaging can be used to investigate atrial fibrillation?


  • Echocardiogram to see if there is a cardiac cause of AF (e.g., left atrial dilatation secondary to mitral valve disease)
• When should emergency admission or cardiology referral be considered for atrial fibrillation?


  • New-onset AF within the past 48 hours and is haemodynamically unstable
  • Severe symptoms due to rapid (bpm > 150) or very slow (bpm < 40) ventricular rate
  • Concomitant acute decompensated heart failure
  • Complications such as TIA/stroke
  • Acute, potentially reversible triggers (e.g., pneumonia/sepsis or thyrotoxicosis)
• What is the management for patients with atrial fibrillation who do not require acute management?


  They can be considered for outpatient management